Date: Thu, 9 Feb 2006 23:17:03 -0800
From: Andrew Morton <akpm@osdl.org>
To: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
Cc: kernel@kolivas.org, npiggin@suse.de, mingo@elte.hu, rostedt@goodmis.org,
       pwil3058@bigpond.net.au, suresh.b.siddha@intel.com,
       linux-kernel@vger.kernel.org, torvalds@osdl.org
Subject: Re: [rfc][patch] sched: remove smpnice
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"Siddha, Suresh B" <suresh.b.siddha@intel.com> wrote:
>
> On Tue, Feb 07, 2006 at 03:36:17PM -0800, Andrew Morton wrote:
> > Suresh, Martin, Ingo, Nick and Con: please drop everything, triple-check
> > and test this:
> > 
> > From: Peter Williams <pwil3058@bigpond.net.au>
> > 
> > This is a modified version of Con Kolivas's patch to add "nice" support to
> > load balancing across physical CPUs on SMP systems.
> 
> I have couple of issues with this patch.
> 
> a) on a lightly loaded system, this will result in higher priority job hopping 
> around from one processor to another processor.. This is because of the 
> code in find_busiest_group() which assumes that SCHED_LOAD_SCALE represents 
> a unit process load and with nice_to_bias calculations this is no longer 
> true(in the presence of non nice-0 tasks)
> 
> My testing showed that 178.galgel in SPECfp2000 is down by ~10% when run with 
> nice -20 on a 4P(8-way with HT) system compared to a nice-0 run.
> 
> b) On a lightly loaded system, this can result in HT scheduler optimizations
> being disabled in presence of low priority tasks... in this case, they(low
> priority ones) can end up running on the same package, even in the presence 
> of other idle packages.. Though this is not as serious as "a" above...
> 

Thanks very much for discvoring those things.

That rather leaves us in a pickle wrt 2.6.16.

It looks like we back out smpnice after all?

Whatever we do, time is pressing.
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